TensorFlow Cannot feed value of shape (100, 784) for Tensor 'Placeholder:0'

Question

I am learning TensorFLow. So to understand how to make something, I tried to copy some code from a source and execute it. But I\'m hitting an error message. So I tried some

Answer 1

You need to reshape X.

    X = tf.placeholder(tf.float32 , [None ,28 , 28 , 1])
    X = tf.reshape(X , [-1 , 784])

Answer 2

When you define a placeholder in TensorFlow, the shape of the input during the session should be the same as the shape of the placeholder.

In batch_X, batch_Y = mnist.train.next_batch(100), the batch_x is a 2D array of pixel values, which will have a shape of [batch_size, 28*28].

In X = tf.placeholder(tf.float32,[None, 28, 28, 1]), the input placeholder is defined to have a 4D shape of [batch_size, 28, 28, 1]

You can either 1) reshape batch_x before the feeding to TensorFlow. e.g.batch_x = np.reshape(batch_x, [-1, 28, 28, 1]) or 2) Change the shape of the placeholder. e.g. X = tf.placeholder(tf.float32,[None, 784])

I would recommend 2), since this saves you from doing any reshaping operations both in and outside of the TensorFlow graph.

Answer 3

You are getting that error because there is a mismatch between the shape of what you are feeding in and what the TensorFlow is expecting. To fix the issue, you might want to reshape your data at placeholder:0 which is batch_X to (?, 28, 28, 1). For example, you would do the following:

batch_X = np.reshape(batch_X, (-1, 28, 28, 1))